The common input device of a computer system includes for example a mouse, a keyboard or a trackball. In particular, for most users, the keyboard becomes an indispensable input device of the computer system. Via the keyboard, the user may input characters and instructions into the computer system.
FIG. 1 is a schematic view illustrating the outward appearance of a conventional keyboard. The surface of the keyboard 1 includes plural keys. These keys include ordinary keys 10, numeric keys 11 and function keys 12. When one or more keys are depressed by the user, a corresponding signal is issued to the computer, and thus the computer executes a function corresponding to the depressed key or keys. For example, when the ordinary keys 10 are depressed, corresponding English letters or symbols are inputted into the computer system. In addition, the function keys 12 (F1˜F12) can be programmed to cause corresponding application programs to provide certain functions.
Hereinafter, the internal circuitry of the conventional keyboard device will be illustrated with reference to FIG. 2. FIG. 2 is a schematic circuit diagram illustrating the internal circuitry of the conventional keyboard. The keyboard 1 includes a controlling unit 13 and a keyboard scanning matrix 14. The controlling unit 13 is connected with plural input/output (I/O) ports through multiple pins. Generally, the controlling unit 13 is a microprocessor. The other parts of the microprocessor are known in the art, and are not redundantly described herein. The keyboard scanning matrix 14 includes plural I/O ports (X0˜X7 and Y0˜YG). These I/O ports crisscross to define the keyboard scanning matrix 14. As shown in FIG. 2, since the keyboard scanning matrix 14 is an 8×16 matrix, there are a total of 128 key intersection points corresponding to 128 keys on the surface of the keyboard 1. In other word, if there are 128 keys on the surface of the keyboard 1, the internal circuit of the keyboard device 1 should have at least 24 I/O ports.
With the maturity of computing technologies, the keyboard with basic functions fails to meet the users' requirements. For this reason, the keyboard manufacturers make efforts in designing novel keyboards with diversified functions. Recently, a pressure sensitive keyboard having a pressure sensing function has been disclosed. In the pressure sensitive keyboard, a pressure sensing module is disposed under the plural keys for sensing the pressure exerted on the key that is depressed by the user. Generally, the pressure sensitive keyboard has a preset pressure value. In a case that the pressure exerted on the depressed key is lower than the preset pressure value, the pressure sensitive keyboard issues a first sensing signal. In response to the first sensing signal, the computer executes a first instruction. Whereas, in a case that the pressure exerted on the depressed key is higher than the preset pressure value, the pressure sensitive keyboard issues a second sensing signal. In response to the second sensing signal, the computer executes a second instruction.
Take a process of inputting a character to a Notepad document for example. The key to be depressed is the key A. In a case that a first pressure lower than the preset pressure value is exerted on the key A, a small letter “a” is shown on the Notepad document in response to the depressing action of the user. Whereas, in a case that a second pressure higher than the preset pressure value is exerted on the key A, a capital letter “A” is shown on the Notepad document in response to the depressing action of the user.
Although the conventional pressure sensitive keyboard has good practicability, there are still some drawbacks. For example, the new users or uneducated users of the pressure sensitive keyboard usually fail to judge whether the pressure exerted on the depressed key is higher than the preset pressure value or not. That is, when a key is depressed, the users usually fail to realize which instruction will be executed by the computer. Therefore, there is a need of proving a pressure sensitive keyboard having a function of recognizing the strength of the pressure exerted on the depressed key.